A purchaser of a computer type system such as a telephone switching system often purchases the system with certain optional features, but later wishes to add to them. Such features have been provided by selling hardware modules or software upgrades. However such means for adding options is cumbersome, since the supplier must estimate the likely number of upgrades to be purchased within a reasonable future time, and which upgrades are likely to be purchased, and then manufacture and stock hardware option modules or floppy disks carrying software upgrades for those options.
In addition, hardware and software piracy of the modules or software is also a large problem and difficult to detect and to stop.